/**

* Solution 1: use two queues;

* Solution 2: use only one queue;

* Solution 3:

*/

class MyStack {

private Queue<Integer> qFront = new LinkedList<Integer>();

private Queue<Integer> qBack = new LinkedList<Integer>();

// Push element x onto stack.

public void push(int x) {

qBack.add(x);

}

// Removes the element on top of the stack.

public void pop() {

if (qBack.isEmpty()) {

while (!qFront.isEmpty()) {

qBack.add(qFront.poll());

}

}

while (qBack.size() != 1) {

qFront.add(qBack.poll());

}

// get rid of the last one (stack top).

qBack.poll();

}

// Get the top element.

public int top() {

if (qBack.isEmpty()) {

while (!qFront.isEmpty()) {

qBack.add(qFront.poll());

}

}

while (qBack.size() != 1) {

qFront.add(qBack.poll());

}

return qBack.peek();

}

// Return whether the stack is empty.

public boolean empty() {

return qBack.isEmpty() && qFront.isEmpty();

}

}

// Solution 2:

class MyStack {

private Queue<Integer> queue = new LinkedList<Integer>();

// Push element x onto stack.

public void push(int x) {

queue.add(x);

for (int i = 0; i < queue.size() - 1; i++) {

queue.add(queue.poll());

}

}

// Removes the element on top of the stack.

public void pop() {

queue.poll();

}

// Get the top element.

public int top() {

return queue.peek();

}

// Return whether the stack is empty.

public boolean empty() {

return queue.isEmpty();

}

}